Electrophotographic photoreceptors are available in two types: one based on inorganic photoconductive material and the other based on organic photoconductive material. With advantages such as freedom of environmental pollution, high productivity and low cost, organic photoconductive materials have recently been used commonly.
Of the organic photoconductive materials, those which generate charges upon visible light absorption are poor in charge retentivity, while those having good retentivity and excellent film-formability are generally poor in visible light photoconductivity. To solve this problem, it is common practice to functionally separate the light-sensitive layer into a charge generation layer (CGL) which absorbs visible light and generates a charge and a charge transport layer (CTL) which transport the charge. This allows separate choice of charge generation material (CGM) and charge transport material (CTM), affording broader ranges of criteria for choosing respective materials.
Conventional CGMs include polycyclic quinone pigments, perillene pigments, indigo pigments, bisbenzimidazole pigments, quinacridone pigments, phthalocyanine pigments, monoazo pigments, disazo pigments, trisazo pigments and polyazo pigments. Conventional CTMs include amine compounds, hydrazone compounds, pyrazoline compounds, oxazole compounds, oxadiazole compounds, stilbene compounds and carbazole compounds. For example, the use of perillene pigments as CGMs is disclosed in Japanese Patent Examined Publication No. 5423/1986 and Japanese Patent Publication Open to Public inspection (hereinafter referred to as Japanese Patent O.P.I. publication) Nos. 192958/1982, 59686/1984 and 122954/1985.
In addition to CGL and CTL, auxiliary layers such as a barrier layer (BAL), a protective layer and an adhesive layer and the order of their coating are being investigated.